1. Field of the Invention
This invention relates to luminaires or light reflecting systems and more specifically to the reflectors of such systems and their manufacture to produce versatile or adjustable reflectors approximating parabolic reflectors at relatively low cost.
2. Description of the Prior Art
Light reflectors are employed in luminaires to concentrate light in a generally desired direction. Reflectors are placed behind the source of light and are normally concave in shape so as to permit all light emanating from the light and reflector system to be either the direct light from the source or to be the primary reflective light. Primary reflective light is that light which is reflected only once from the source before the light is emitted from the luminaire.
One of the most efficient light reflectors known is in the shape of an elliptic paraboloid. The surface of an elliptic paraboloid may be formed by revolving a parabola about its axis. An important optical property of a parabola is that it will primarily reflect in parallel or collimated rays all light directed to it from a source located at its focus, these rays being parallel to the axis, in this case the "optical" axis of the parabola. In three dimensional terms, a paraboloid of revolution has the same desirable properties.
Although light reflectors have been successfully produced shaped like a paraboloid of revolution, several drawbacks are noted in such prior art reflectors. First, a reflector having a smooth concave shape is normally fabricated from molding or otherwise conforming a flat piece of metal. Again, normally the reflective surface of a reflector are made of specular Alzak, which becomes dull the more it is worked. Other reflector materials suffer this same disadvantage. Furthermore, forming a reflector surface is generally a much more expensive fabrication technique than bending and cutting. This is especially true for reflectors that are somewhat large, as for use with sodium vapor, metal halide and mercury vapor lamps.
Second, a paraboloid of revolution may concentrate the light too much for many applications. A highly concentrated beam is desirable for a search light application, but not for general illumination.
Third, a perfect paraboloid of revolution provides a relatively inflexible reflector. Although the light source may be moved from the focus, doing so may cause undesirable reflections. When the source is moved away from the focus along the axis, the beam is either caused to spread (non-parallel rays diverging) or caused to merge (non-parallel rays converging). When the source is mislocated off its axis, then the reflections from a relatively near surface is reflected at one angle while a relatively far surface is reflected at another, causing spreading in a non-uniform fashion. Such a repositioning does not refocus the beam so as to keep the beam desirably a parabolic-type reflection.
It is therefore a feature of this invention to provide an improved light reflector which is readily fabricated approximating a plurality of partial paraboloids of revolution.
It is another feature of this invention to provide an improved light reflector readily fabricated from flat reflective material comprising segments and facets, the reflector being conveniently adjustable to aproximate a plurality of parabolic surfaces.
It is still another feature of this invention to provide an improved light reflector having a cross section in the form of an arc which approximates a range of parabolas having different focus directions and hence, with a complementary reflector, achieving an overall capability of reflecting a change of beam widths, the reflections operating particularly efficiently with appreciable lighted lengths, rather than with theoretical, but non-existing, point sources.